1. Field of the Invention
The invention relates generally to a tool for use in an oilfield wellbore, and more specifically to an easily replaceable electrical device for use in such a tool.
2. Description of the Related Art
Tools requiring electrical power are often used for conducting various operations in a wellbore. This creates a need for portable electrical power, preferably power that can be mounted directly onto a downhole tool. One way of providing electrical power downhole is through the use of a battery pack. Typically, the battery pack is constructed of multiple cells mounted in rigid plastic, epoxy, fiberglass, or aluminum shells and is housed in a sonde or in an annular housing mounted in the bore of a downhole tool. One or more cells are typically contained within the battery pack. The cells can be electrically connected in various series or parallel configurations to provide the necessary voltage and current capacities required for the various loads. The cells generally are immobilized inside the battery pack by an epoxy. In order to change the battery pack in the downhole tool, the tool has to be disassembled. Disassembly of the tool makes replacing a battery pack time consuming and, in certain cases, is impossible at the job site. For quicker job turnaround, it is desirable that the battery be replaceable without requiring tool disassembly and without the use of specialized equipment typically not available at the job site.
The methods and apparatus of the present invention overcome the foregoing disadvantages of the prior art by providing an externally replaceable battery pack that does not require major tool disassembly.
In general, in one aspect of the present invention, a downhole tool for use in a wellbore, comprises a tubular member, such as a drill collar housing, in a drill string. The tubular member has at least one cavity formed on an external surface. A housing is adapted to insert in and extract from the cavity. The housing has at least one electrical device, such as a battery stack, disposed within the housing.
In another aspect of the present invention, sensors are disposed in the housing for measuring downhole parameters of interest including, but not limited to, annulus pressure and annulus temperature.
In another embodiment, a replaceable battery pack for a downhole tool in a wellbore, comprises a housing adapted to be insertable in and extractable from a cavity on an external surface of the downhole tool, and has at least one electrical power cell disposed in the housing.
In one aspect, a method of replacing an electrical device in a downhole tool, comprises removing a first housing containing the electrical device from a cavity on an external surface of the downhole tool, and installing a second housing containing a second electrical device in the cavity without disassembling the tool further.
In yet another embodiment, a method of replacing a battery pack in a downhole tool, comprises removing a first housing containing a plurality of electrical power cells from a cavity on an external surface of the downhole tool, and installing a second housing containing a second plurality of electrical power cells in the cavity without disassembling the tool further.
Examples of the more important features of the invention thus have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto.